DivJ: Galaxies and Cosmology During the Division Days

An artist’s impression of the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters. (ESO/M. Kornmesser. Courtesy from ESO Press Release October 2014 (Dannerbauer et al. 2014, Astronomy & Astrophysics, 570, 55)

Scientific Role of Division J

Division J covers nearly all of the physical processes of the Universe, with some topics overlapping those of Division D, High Energy Phenomena and Fundamental Physics.

The four primary topics for Division J are:

Physics and content of the Universe

Evolution of structures

Formation and evolution of galaxies

Spatially resolved galaxies

Dedicated studies during the past decade have been performed on galaxy clusters, which trace the formation of the most massive dark matter halos and their components, such as galaxies, intracluster medium and dark matter. A crucial epoch for galaxy evolution and formation is the first billion years of the Universe, when there was enhanced star-formation and black hole activity compared with the local Universe, as well as a huge increase of stellar mass, both in cluster and field galaxies.

Despite significant recent advances within this research field, there are still key questions that remain unanswered:

When and how did present-day galaxy clusters form in the distant Universe?

Are the overall properties of large-scale structures consistent with model predictions?

How does galaxy environment affect the conversion of molecular gas into stars?

Over the past two decades a number of selection techniques and tools have been developed to search for clusters at different redshifts and evolutionary stages. These techniques span the whole of the electromagnetic spectrum, are sensitive to different physical properties and effects and have produced a so-called “protocluster zoo“. The number of known protoclusters beyond z=2 still remains small, which introduces substantial uncertainty and selection bias into our findings.

The advancement of space missions, coupled with the construction of next-generation ground-based telescopes and instruments, will improve this situation dramatically; we expect the number of observed protocluster systems to increase from single digits to several hundreds or thousands.

Organisation of Division J

We are also happy to announce that Inter-Division D-G-H-J Commission, Galaxy Spectral Energy Distributions, will continue through the 2018-2021 term. The diversity of physical phenomena and the variety of components (for example, stars, gas, AGN, dust and cosmic rays) producing a given spectral energy distribution (SED) requires interactions between multiple communities and topics.

A further three IAU Commissions participate in Division J activities:

Inter-Division G-H-J Commission: Stellar Clusters throughout Cosmic Space and Time

Finally, as the number of small and large projects dedicated to building libraries of modelled or observed SED continues to grow, as do the sizes of the data libraries themselves, two new Working Groups have been established:

General Assembly Scientific Programme for Division J

Seven sessions have been reserved for Friday, 24 August and Monday, 27 August for Division J topics. The first session on Friday morning covered general Division matters, poster presentations and two talks by PhD prize winners Fabio Pacucci (Yale University, US) and Max Gronke (University of California, Santa Barbara, US).

Five sessions have been allocated to a mini-symposium on the formation of galaxy clusters, “Build-up of Galaxy Clusters”, which will focus on two key topics in this research field: protocluster assembly and protocluster searches, and star formation in clusters across cosmic time.

The final Division Days session is scheduled as a business meeting of the Inter-Division D-G-H-J Commission, Galaxy Spectral Energy Distributions, at which initial reports will be presented from the two new Working Groups of Division J.

CLAUS LEITHERER, outgoing President of Division J, is Head of the Science Policies Group at the Space Telescope Science Institute. His research interests include the formation and evolution of massive stars and the stellar populations of galaxies..

DENIS BURGARELLA, incoming President of Division J, studies galaxies at high redshifts using Code Investigating GALaxy Emission (CIGALE) at Laboratoire d’Astrophysique de Marseille, France. From 2015 to 2018, he was the President of Commission J1 and he is also a member of the Division J organising committee.

HELMUT DANNERBAUER did his PhD thesis at the Max Planck Institute for Extraterrestrial Physics. He is now based at the Instituto Astrofísica de Canarias at Tenerife, Spain, where he studies galaxies in the early Universe, primarily based on observations in the far-infrared and radio wavelength regime.